Hepatitis A virus has been successfully transmitted to marmosets and chimpanzees. Infection results in biochemical and histopathological evidence of hepatitis in both species. Since both of these species are difficult to obtain, several other species of primates more readily available are under investigation as possible models. In studies with chimpanzees inoculated with different subtypes of hepatitis B, preliminary results indicate infection with one subtype of HBV confers partial, if not complete, protection against rechallenge with another subtype. We have experienced difficulties with our studies of hepatitis B in Rhesus monkeys because of an inability of demonstrate successful transmission in recent experiments. Attempts to resolve this problem are in progress.